Not Applicable.
1. Field of the Invention
This invention relates to seals used in the oil and gas industry, and more particularly to a high pressure liner packer seal. In one aspect, the invention relates to radially expandable rings for use in a packer to achieve a seal of an inner tubular within a casing, for example, a well bore casing.
2. Description of the Related Art
A typical well bore has an outer tubular therein that by way of example is borehole casing. Pipe string is tripped, or run, into the well bore through the outer tubular and will typically have various subs and tools connected in-line in the string for performing various tasks in the well. In the drilling and completion of oil and gas wells, the annulus between the well bore casing and an interior tubular, for example a work string or a production string, is commonly required to be sealed. One type of such an annular seal is referred to as a packer. Packers operate with an un-set, or run-in, diameter while tripped to the desired location in the well bore. The packers are then are expanded radially outward to a set position diameter by some mechanism to seal against the inside of the well bore casing.
Packers often employ elastomeric seals. However, elastomeric seals suffer from several drawbacks. They often cannot withstand prolonged high temperature and/or high pressure. The seals may also extrude into gaps, sacrificing the sealing quality. Additionally, elastomeric seals are highly susceptible to xe2x80x9cswabbing offxe2x80x9d of the packer when the packer is tripped down hole due to axial forces from the fluid flow across the elastomeric seal. xe2x80x9cswabbing offxe2x80x9d also occurs when high circulating flow rates are used to clean the wellbore of debris or xe2x80x9cmud cakexe2x80x9d prior to cementing cause high axial forces across the elastomeric seal. Elastomeric seals are also subject to eventual deterioration after prolonged exposure to corrosive fluids and high temperatures. Also, when energized, elastomeric seals are likely to flow along extrusion pathways if unchecked.
Metal components can be used to obtain gas tight metal-to-metal seals, but are generally only suited for rather pristine environments other than wellbores. One problem with metal sealing components is that, like elastomeric components, metal sealing components will eventually become degraded after prolonged exposure to corrosive fluids.
A need exists for an expandable seal that can seal the annulus between the well bore casing and an inner tubular without the drawbacks of the conventional metal to metal seals or the conventional elastomeric seals. A need also exists for a packer metal to metal seal that can conform to out of round casing for proper sealing.
Hence, it is desired to provide a high performance sealing apparatus with a high flow-by and a high differential element. It is further desired to provide a sealing apparatus with a self-energizing, non-extrusion seal element design. It is a further object of this invention to provide a sealing apparatus that allows fast tripping into a well bore with an anti-swabbing off sealing element design.
Other objects, features and advantages of the invention will be apparent from the following detailed description taken in connection with the accompanying drawings.
The preferred embodiment relates to a sealing apparatus for sealing an annulus between a mandrel and an inner surface of an outer tubular. The apparatus comprises a top seal ring and a bottom seal ring separated by a double-ramped cylinder, all of which are mounted on the outer diameter (OD) of the mandrel and fit within the inner diameter (ID) of the outer tubular. The sealing apparatus is capable of being positioned in different modes. One mode is the running in, xe2x80x9ctripping inxe2x80x9d mode and is used when the seal assembly is being located down hole in the outer tubular. Another mode is the set position mode where the seal rings are expanded to seal the annulus between the mandrel and the outer tubular.
The top and bottom seal rings each comprise a base with an extending expandable arm. The seal rings also each comprise an elastomeric material that covers the OD of at least the expandable arm. The base of each seal ring also comprises an inner seal that forms a fluid-tight seal between the inner surface of the base and the OD of the mandrel. The expandable arms each comprise a leading edge notch and a back-up extension. The leading edge notch is designed to fail by bending or shearing under a smaller load than the bending or shearing load for the top seal ring notch. The expandable arms also comprise an inner shoulder at the expandable arm base. The elastomeric materials cover the outer surface of each expandable arm, but with the back-up extensions extending through the elastomeric materials. The top and bottom seal rings are positioned on the mandrel such that the expandable arms face each other.
The double-ramp cylinder moveably engages the mandrel and is positioned between the top seal ring and bottom seal ring. The double-ramp cylinder comprises a top ramp surface and a bottom ramp surface. The ramp surfaces taper in towards the mandrel as they approach the top and bottom seal rings, respectively. At the end of each ramp surface is a shoulder.
In operation, the sealing apparatus is placed on the mandrel in the running in position. The mandrel includes a shoulder that prevents the bottom seal ring from sliding relative to the mandrel in the downhole direction. The mandrel and sealing apparatus are then placed downhole in the outer tubular. Once at the desired location, a load is applied to the uphole end of the top seal ring. This in turn places a load on the double-ramped cylinder through the top seal ring notch acting against the shoulder on the top ramp surface. The load further acts on the bottom seal ring through the shoulder on the bottom ramp surface acting against the bottom seal ring notch. The load is preferably applied mechanically.
Once the load reaches a predetermined magnitude, the bottom seal ring notch shears or bends, causing the bottom ramp surface to slide under and expand the expandable arm of the bottom seal ring. As the bottom seal ring expandable arm expands, the elastomeric material and the back-up extension form a pressure-tight seal against the ID of the outer tubular. Additional load placed on the top seal ring causes the top seal ring notch to shear or bend, causing the top seal ring expandable arm to slide over the top ramp surface and expand. As the top seal ring expandable arm expands, the elastomeric material and the back-up extension form a pressure-tight seal against the ID of the outer tubular. Once in the set position, the top seal ring thus additionally seals the annulus between the mandrel and the outer tubular.
Thus, the preferred and alternative embodiments comprise a combination of features and advantages that enable them to overcome various problems of prior devices. The various characteristics described above, as well as other features, will be readily apparent to those skilled in the art upon reading the following detailed description of the preferred and alternative embodiments, and by referring to the accompanying drawings.